Quantifying the detection likelihood of faint peaks in interferometric data through jackknifing

Astronomy and Astrophysics, vol. 695, pp. A204

Abstract

Context. False-positive emission-line detections bias our understanding of astronomical sources; for example, falsely identifying z ∼ 3–4 passive galaxies as z > 10 galaxies leads to incorrect number counts and flawed tests of cosmology. Aims. In this work, we provide a novel but simple tool to better quantify the detection of faint lines in interferometric data sets and properly characterize the underlying noise distribution. We demonstrate the method on three sets of archival observations of z > 10 galaxy candidates, taken with the Atacama Large Millimeter/Submillimeter Array (ALMA). Methods. By jackknifing the visibilities using our tool, jackknify, we create observation-specific noise realizations of the interferometric measurement set. We apply a line-finding algorithm to both the noise cubes and the real data and determine the likelihood that any given positive peak is a real signal by taking the ratio of the two sampled probability distributions. Results. We show that the previously reported, tentative emission-line detections of these z > 10 galaxy candidates are consistent with noise. We further expand upon the technique and demonstrate how to properly incorporate prior information on the redshift of the candidate from auxiliary data, such as from the James Webb Space Telescope. Conclusions. Our work highlights the need to achieve a significance of ≳ 5σ to confirm an emission line when searching in broad 30 GHz bandwidths. Using our publicly available method enables the quantification of false detection likelihoods, which are crucial for accurately interpreting line detections.

Authors 9

1. Joshiwa van Marrewijk Aachen Leiden Observatory

   Leiden University · European Southern Observatory · Leiden Observatory

   Affiliation as printed

   European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching, Germany

   Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands

2. Melanie Kaasinen

   European Southern Observatory

   Affiliation as printed

   European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching, Germany

3. Gergö Popping

   European Southern Observatory

   Affiliation as printed

   European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching, Germany

4. Luca Di Mascolo

   Centre National de la Recherche Scientifique · University of Groningen · Université Côte d'Azur · Lagrange Laboratory · Observatoire de la Côte d’Azur

   Affiliation as printed

   Kapteyn Astronomical Institute, University of Groningen, Landleven 12, 9747 AD Groningen, The Netherlands

   Laboratoire Lagrange, Université Côte d'Azur, Observatoire de la Côte d'Azur, CNRS, Blvd de l'Observatoire, CS 34229, 06304 Nice cedex 4, France

5. Tony K. Mroczkowski

   European Southern Observatory

   Affiliation as printed

   European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching, Germany

6. Leindert Boogaard Aachen Leiden Observatory

   Leiden University · Max Planck Institute for Astronomy · Leiden Observatory

   Affiliation as printed

   Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands

   Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany

7. Francesco Valentino

   European Southern Observatory

   Affiliation as printed

   European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching, Germany

8. Tom J. L. C. Bakx

   Chalmers University of Technology

   Affiliation as printed

   Department of Space, Earth, & Environment, Chalmers University of Technology, Chalmersplatsen 4, 412 96 Gothenburg, Sweden

9. Ilsang Yoon

   National Radio Astronomy Observatory

   Affiliation as printed

   National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903, USA